81305765 has 4 divisors (see below), whose sum is σ = 97566924. Its totient is φ = 65044608.

The previous prime is 81305753. The next prime is 81305767. The reversal of 81305765 is 56750318.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 42393121 + 38912644 = 6511^2 + 6238^2 .

It is a cyclic number.

It is not a de Polignac number, because 81305765 - 2⁶ = 81305701 is a prime.

It is a super-2 number, since 2×81305765² = 13221254844470450, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81305767) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8130572 + ... + 8130581.

It is an arithmetic number, because the mean of its divisors is an integer number (24391731).

Almost surely, 2^81305765 is an apocalyptic number.

It is an amenable number.

81305765 is a deficient number, since it is larger than the sum of its proper divisors (16261159).

81305765 is a wasteful number, since it uses less digits than its factorization.

81305765 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16261158.

The product of its (nonzero) digits is 25200, while the sum is 35.

The square root of 81305765 is about 9016.9709437261. The cubic root of 81305765 is about 433.2186188787.

The spelling of 81305765 in words is "eighty-one million, three hundred five thousand, seven hundred sixty-five".